The major objective is to investigate the development of mastery motivation in the first year of life. Three aspects of mastery were distinguished: persistence in problem solving, in practicing emerging sensorimotor skills, and in obtaining feedback from the objects. The interrelationships among these components of mastery are being explored, and the origins of mastery and its continuity over time are being studied. The sample includes 75 infants from middle income families. Several methods are being employed--twelve tasks to measure mastery motivation; observation of mother-infant and father-infant interaction in the home; Bayley Scales of Infant Development and parent perception of infant temperament. With regard to the continuity of mastery behaviors, meaningful transformations have been found between 6 and 12 months of age. The interrelations between mastery motivation and cognitive development are complex. Mastery motivation influences cognitive development, and the level of cognitive functioning in turn influences mastery motivation.